This Program Project deals with experimental leukemogenesis. Callaborative investigations of cellular and virological mechanisms related to leukemogenesis are proposed. The expression of endogenous Type C RNA viruses by lymphocytes in various stages of differentiation will be analyzed and related to the development of leukemia. Neoplastic and normal lymphocytes will be used to identify and analyze cells that are targets of transforming viruses. Virus expression by cells in different stages of malignant transformation will be ascertained. The contribution of lymphocyte differentiation to the formation of recombinant viruses will be determined. The genetic structure of the latter agents will be determined and related to their biological effects. Transforming and non-transforming avian oncornoaviruses will be used to determine structure-function relations of src genets.